Two possible ideas: 1. Cannons are produced with 3 crew members that are attached to the cannon for always. Only one health bar for everything - including the crew members and the cannon itself - the health bar reaches zero: the crew dies and the cannon gets destroyed. Easy thing, just a visual feature. Cannons may get captured with their crew. (one unit) 2. Cannons are built as cannons only and crew members are hired in the barracks and occupy any artillery unit. Crew could die, cannon needs new crew member(s) to be operated again. Gun destroyed, crew alive but worthless, may occupy a new cannon. Cannons can only be captured when the crew is dead or no crew assigned. Both models have their advantages but regarding the unpopular (sometimes) micro management I would prefer the first design.